feat: add --separate-scratch flag

[patrickhoefler]

This pull request introduces several changes to improve the functionality, testing, and maintainability of the dockerfile2dot tool. The most significant updates include the addition of a --separate-scratch flag to handle scratch images uniquely, refactoring to use ID instead of Name for external image identification, and enhancements to the testing guidelines and code quality documentation.

New Feature: --separate-scratch Flag

• Added a --separate-scratch flag to create separate nodes for each scratch image in the graph instead of collapsing them. This includes updates to the CLI (internal/cmd/root.go) and corresponding tests (internal/cmd/root_test.go). [1] [2] [3] [4] [5] [6]

Refactoring: External Image Identification

• Refactored to use ID instead of Name for identifying external images, ensuring unique identification and improving maintainability. Changes span multiple files including internal/dockerfile2dot/build.go, internal/dockerfile2dot/convert.go, and their respective tests. [1] [2] [3] [4] [5] [6] [7]

Documentation and Testing Guidelines

• Added a new .github/copilot-instructions.md file outlining testing guidelines and code quality standards, emphasizing clean testing, proper assertions, and consistent naming conventions.

Build Process Improvements

• Introduced a check target in the Makefile that runs both linting and tests, streamlining the build process.

Minor Enhancements and Fixes

• Updated addExternalImages to handle the separateScratch flag, ensuring unique IDs for scratch instances and avoiding duplicate entries. [1] [2]
• Adjusted test cases in internal/dockerfile2dot/convert_test.go to align with the new ID-based external image identification and the --separate-scratch functionality. [1] [2] [3]

[Copilot]

Pull Request Overview

This PR adds a new --separate-scratch flag to control whether scratch images are collapsed into one node or kept separate, refactors external-image handling to use unique IDs, and updates tests, documentation, and the build system accordingly.

• Introduce --separate-scratch flag in CLI and propagate through parsing and graph generation
• Refactor ExternalImage and WaitFor to include an ID field and update all references
• Enhance tests and documentation; add a check Makefile target

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/dockerfile2dot/structs.go	Added ID fields and improved comments
internal/dockerfile2dot/load.go	Updated function signature to accept separateScratch
internal/dockerfile2dot/load_test.go	Simplified test to only check error, removed output assertions
internal/dockerfile2dot/convert.go	Propagate separateScratch flag and update external images logic
internal/dockerfile2dot/convert_test.go	Added separateScratch cases and updated expected IDs
internal/dockerfile2dot/build.go	Use waitFor.ID instead of name when creating edges
internal/dockerfile2dot/build_test.go	New test for separate-scratch graph labels
internal/cmd/root.go	Register --separate-scratch flag
internal/cmd/root_test.go	CLI integration test for the new flag
README.md	Documented the new flag
Makefile	Added check target
.github/copilot-instructions.md	Added testing and quality guidelines

Comments suppressed due to low confidence (2)

internal/dockerfile2dot/load_test.go:54

• The test no longer verifies the returned SimplifiedDockerfile value, reducing coverage of parsing logic. Consider reintroducing assertions (e.g., using cmp.Diff or explicit field checks) to validate the parsed output.

			_, err := LoadAndParseDockerfile(

README.md:157

• The indentation of the --separate-scratch entry doesn’t align with the other flags; adjust leading spaces so it lines up consistently in the flags list.

      --separate-scratch        create separate nodes for each scratch image instead of collapsing them